Effect of Sintering Temperature on the Microstructure and Mechanical Properties of Nanocrystalline Cemented Carbide

WC-Co nanocrystalline nitrogen-containing cemented carbides were prepared by vacuum sintering and low pressure sintering.The sintering processes of Cr_(2)(C,N)doped nano WC-Co powders were studied by using thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).The effect of sintering temperature on the microstructure and mechanical properties of nanocrystalline cemented carbide was studied by scanning electron microscope(SEM),high resolution transmission electron microscope(HRTEM)and mechanical property test.The results showed that the nano WC grains began to grow in the solid phase sintering stage.A high-performance nano-nitrogen-containing cemented carbide with uniform microstructure and good interfacial bonding can be obtained by increasing the sintering temperature to 1380℃.It has a transverse rupture strength(TRS)of 5057 MPa and a hardness of 1956 HV30.

Comparative Study on Microstructure and Mechanical Properties of Coarse-grained WC-based Cemented Carbides Sintered with Ultrafine WC or (W+C) as Additives

The effects of ultrafine WC(WC_(UF),0.5μm) or W(1μm) and C(0.3μm)(W+C)_(UF) additives on the densification,microstructure and mechanical properties of coarse-grained cemented carbides were compared systematically.Overall,the cemented carbides with WC_(UF)/(W+C)_(UF) additives are almost fully densification to be higher than 99%,and the average grain size is kept above 2.8μm.The WC_(UF) additive assists grains to(truncated)trigonal prism shape by two dimensional(2D) growth,whereas the(W+C)_(UF) additive assists grains to rounded shape by three dimensional(3D) growth,lowers WC contiguity and increases face-centered-cubic Co.The hardness and bending strength of(75WC_(C)-15WC_(UF))-10Co are 86.6 HRA and 2 272 MPa,respectively,both higher than those of(75WC_(C)-15(W+C)_(UF))-10Co,which could be ascribed to the enhanced densification and unblemished grains.However,the fracture toughness of the(75WC_(C)-15(W+C)_(UF))-10Co is 23.5 MPa·m^(1/2),higher than that of the(75WC_(C)-15WC_(UF))-10Co due to the uniform WC-Co structure and flexible binder phase.

Microstructure and mechanical properties of(Ti,Al,Zr)N/(Ti,Al,Zr,Cr)N films on cemented carbide substrates

（Ti,Al,Zr）N/（Ti,Al,Zr,Cr）N bilayer films were deposited on cemented carbide （WC-8%Co） substrates by multi-arc ion plating （MAIP） using two Ti-AI-Zr alloy targets and one pure Cr target. To investigate the composition, morphology, and crystalline structure of the bilayer films, a number of complementary methods of elemental and structural analysis were used, namely, scanning electron microscopy （SEM）, energy disperse X-ray spectroscopy （EDS）, and X-ray diffraction （XRD）. Adhesive strength and mechanical properties of the films were evaluated by scratch testing and Vickers microindentation, respectively. It is shown that the resulting films have a TiN-type face-centered cubic （FCC） structure. The films exhibit fully dense, uniform, and columnar morphology. Furthermore, as the bias voltages vary from -50 to -200 V, the microhardness （max. Hv001 4100） and adhesive strength （max. 〉 200 N） of the bilayer films are superior to those of the （Ti,Al,Zr）N and （Ti,Al,Zr, Cr）N monolayer films.

Sintering characteristics and microstructure of WC-Co-VC/Cr_3C_2 ultrafine cemented carbides

The sintering characteristics, microstructure, and mechanical properties of ultrafine WC-12%Co-0.2%VC/0.5%Cr3C2 cemented carbides were investigated. Dilatometric and differential thermal analyses （DTA） indicate that the compacts start to shrink at 600°C, the shrinkage rate peak is at 1190°C, and the liquid formation temperature is lower than the W-C-Co eutectic temperature （1330°C）. Microstructure analysis results show that the cemented carbides with fine and homogeneous microstructure were obtained when sintered at 1430°C. Continuous and discontinuous grain growth was suppressed due to the synergistic action of VC/Cr3C2. The transverse rupture strength （TRS） of the samples reaches 4286 MPa, with the hardness HRA 92.1. The fine and homogeneous microstructure, alloy strengthening, and different phase constitutions of binder in the cemented carbides result in high hardness and TRS. Continuous and discontinuous grain growth was observed in the cemented carbide sintered at 1450°C, which results in significant decreases of hardness and TRS. It indicates that VC/Cr3C2 additions in the cemented carbides can only suppress the grain growth at a certain temperature.

Effect of VC and NbC additions on microstructure and properties of ultrafine WC-10Co cemented carbides

The nanocomposite WC-Co powders were prepared through planetary ball milling method.Effects of grain growth inhibitor addition and the vacuum sintering parameters on the microstructure and properties of ultrafine WC-10Co cemented carbides were investigated using X-ray diffractometer,scanning electron microscope and mechanical property tester.The results show that VC and NbC additions can refine the WC grains,decrease the volume fraction of Co3W3C phase in ultrafine WC-10Co cemented carbides,and increase the hardness and fracture toughness of the base alloys.After sintering for 60 min at 1 400℃,the average grain size and hardness of ultrafine-grained WC-10Co-1VC cemented carbide are 470 nm and HRA 91.5,respectively.The fracture toughness of cemented carbide WC-10Co-1NbC alloy is over 7 MN·m -3/2 .

FeCoNiTi_(x)中熵合金组织性能及其在硬质合金中的应用

FeCoNi中熵合金相比传统合金具有优异的性能,但其室温强度不高,限制了其应用。通过机械合金化和放电等离子烧结工艺制备FeCoNiTi_(x)(x=0,0.25,0.50,0.75,1)中熵合金块体,重点研究了各元素机械合金化顺序以及Ti含量对FeCoNiTi_(x)中熵合金显微组织和性能的影响,并初步探讨了FeCoNiTi_(x)中熵合金作为黏结剂在WC基硬质合金中的应用。结果表明:机械合金化过程中FeCoNi基体相为FCC相,添加Ti元素后形成Laves相和钛氧化物相,因此FeCoNiTi_(x)中熵合金物相由FCC相、Laves相和钛氧化物相组成。随着Ti含量的增加,FeCoNiTi_(x)合金密度、硬度和强度均上升,塑性先增强后减弱。FeCoNiTi_(0.50)中熵合金表现出良好的力学性能,其显微硬度、屈服强度、压缩强度和压缩应变分别为531 HV、1 987.57 GPa、2 114.85 GPa和20.5%。添加少量Ti元素可提升FeCoNi合金的耐腐蚀性。FeCoNiTi_(x)黏结剂在WC基硬质合金中能稳定存在,抑制WC烧结过程中脱碳相的形成。WC-FeCoNiTi_(0.50)硬质合金表现出较好的力学性能,其显微硬度与断裂韧性分别为1 834 HV与15.12 MPa·m^(1/2)。

以高熵合金作为黏结相的WC基硬质合金的研究进展

WC-Co硬质合金在制造业中应用广泛,高性能、低成本黏结相的选择和设计是当前硬质合金黏结相替代领域的难点和热点。高熵合金(HEA)作为黏结相可细化WC晶粒,提高硬质合金的硬度、断裂韧性、耐腐蚀性和抗氧化性。本文分别从HEA黏结相成分设计、WC-HEA制备技术、微观组织结构、综合性能等方面概述WC-HEA硬质合金的研究进展,阐述了该领域所面临的烧结特性差、易产生相变等问题。以期为HEA作黏结相的强韧化机理的探讨、WC-HEA复合材料的组织-力学性能间构效关系的揭示提供参考。

微量Y_(2)O_(3)对WC−6Co非均匀结构硬质合金微观结构及性能的影响

采用低压烧结法制备了不同Y_(2)O_(3)添加量(质量分数)的WC-6Co非均匀硬质合金,并通过扫描电子显微镜、X射线衍射仪、能谱仪、金相显微镜、电子万能力学试验机、硬度计、矫顽磁力仪等设备研究了Y_(2)O_(3)质量分数对WC-6Co非均匀硬质合金微观结构、相成分及性能的影响。结果表明:Y_(2)O_(3)不会对合金相对密度和相组成产生影响;Y_(2)O_(3)与合金中杂质元素硫、氧等形成稳定的化合物,弥散分散于WC晶界,阻碍WC晶粒的融合长大,降低WC晶粒粒度,抑制WC晶粒非均匀结构的均匀化。随着Y_(2)O_(3)添加量的增加,合金的硬度逐渐增加,而抗弯强度呈现出先迅速上升后下降的趋势。Y_(2)O_(3)质量分数为0.048%对WC-6Co非均匀硬质合金性能提升最明显,硬度和抗弯强度分别达到1530 kgf·mm-2和2902 MPa。

碳含量对超细晶WC-12%Co硬质合金组织及性能的影响

经混料、压形、热等静压烧结制备了8组不同碳含量的WC-12%Co硬质合金,采用金相显微镜、扫描电镜、硬度计、电子万能力学试验机分析了碳含量对合金微观组织及力学性能的影响。结果表明:碳含量为5.26%~5.42%的WC-12%Co硬质合金处于WC+γ二相区;当碳含量小于等于5.22%时,合金出现絮状、针状脱碳相;当碳含量大于等于5.46%时,合金出现黑色絮状的渗碳相,伴有粗晶、粗晶聚集及钴偏析现象。随着碳含量逐渐增加,WC晶粒逐渐长大,结晶趋于完整,晶粒边缘趋于平直化,晶界变得更加清晰,当碳含量达到5.54%时,WC晶粒边缘出现圆角。碳含量为5.26%~5.42%的合金处于WC、Co二相区,综合力学性能较优,硬度维持在1 777~1 695 kg/mm^(2),抗弯强度为3 357~3 290 MPa。

以高熵合金作黏结剂制备硬质合金的现状

自20世纪初问世以来,硬质合金一直是重要的工程材料。采用高熵合金替代Co作黏结剂能提高硬质合金的硬度和耐磨性并降低生产成本。综述了近年来采用高熵合金作黏结剂制备硬质合金的进展,包括制备以高熵合金作黏结剂的硬质合金的碳化物WC和TiC,放电等离子烧结、自蔓延高温合成、真空烧结和热压法等以高熵合金作黏结剂的硬质合金的制备工艺,以及用高熵合金黏结的硬质合金的力学性能、抗高温氧化性能、耐磨性能和耐蚀性能。

Brazing of WC–8Co cemented carbide to steel using Cu–Ni–Al alloys as filler metal: Microstructures and joint mechanical behavior

Three novel Cu-Ni-A1 brazing filler alloys with Cu/Ni weight ratio of 4：1 and 2.5-10 wt% Al were developed and characterized, and the wetting of three Cu-Ni-Al alloys on WC-8Co cemented carbide were investigated at 1190-1210 ℃ by the sessile drop technique. Vacuum brazing of the WC-8Co cemented carbide to SAE1045 steel using the three Cu-Ni-Al alloys as filler metal was further carried out based on the wetting test results. The interfacial interactions and joint mechanical behaviors involving microhardness, shear strength and fracture were analyzed and discussed. The experimental results show that all the three wetting systems present excellent wettability with final contact angles of less than 5 °and fast spreading. An obvious degeneration layer with continuous thin strip forms in the cemented carbide adjacent to the Cu-Ni-A1/WC-8Co interface. The variation of microhardness in the joint cross-section is closely related to the interactions （such as diffusion and solid solution） of WC-8Co/Cu-Ni-Al/steel sys- tem. Compared with the other two brazed joints, the WC-8Co/Cu-19Ni-SAl/steel brazed joint presents more reliable interlayer microstructure and mechanical property while brazing at the corresponding wetting temperatures for 5 rain, and its average shear strength is over 200 MPa after further optimizing the brazing temperature and holding time. The joint shear fracture path passes along the degeneration layer, Cu-Ni-A1/WC-8Co interface and brazing interlayer, showing a mixed ductile-brittle fracture.2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Influence of Deep Cryogenic Treatment on Microstructures and Mechanical Properties of an Ultrafine-Grained WC-12Co Cemented Carbide

Effect of deep cryogenic treatment （DCT） on the microstructures and mechanical behavior of ultrafine-grained WC-12Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co and binder phase Co in cemented carbide were analyzed in detail to correlate the strengthening mechanism with its x -ε, phase transition. The results show that DCT resulted in a slight increase in hardness and bending strength of ultrafine- grained WC-12Co cemented carbide. For the ultrafine-grained cemented carbide after DCT, there is no significant change in the microstructure and the elemental distribution of the cemented carbides, but the fractured morphology shows a feature of plastic deformation. In the cases of pure Co and the binder phase Co in WC-12Co cemented carbide, they exhibit different features of phase transformation. The improvement of mechanical property of cemented carbide can be attributed to the increased amount of ε-Co in WC-12Co composites after DCT.

Microstructure and mechanical properties of titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard, wear-resistant and well-adhesive titanium nitride coatings on cemented carbide cutting tools were prepared by the pulsed high energy density plasma technique at ambient temperature. The results of Auger spectra analysis indicated that the interface between the coating and substrate was more than 250 nm. Under optimized deposition conditions, the highest critical load measured by nanoscratch tester was more than 90 mN, which meant that the TiN film was well adhesive to the substrate; the highest nanohardness and Young抯 modulus according to nanoindentation tests were near to 27 and 450 GPa. The results of cutting tests evaluated by turning hardened CrWMn steel in industrial conditions indicated that the wear resistance and edge life of the cemented carbide tools were enhanced dramatically because of the deposition of titanium nitride coatings. These improvements were attributed to the three combined effects: the deposition and ion implantation of the pulsed plasma and the becoming finer of the grain sizes.

Microstructure and mechanical properties improvements in cemented carbides by(Cr,Mo,Ta)_(2)(C,N) inhibitors

Grain growth inhibitors can effectively suppress the grain size of tungsten carbide(WC),and consequently improve the hardness and strength of the cemented carbides;however,the toughness,one of the most important properties,usually deteriorates with inhibitors.Here,(Cr,Mo,Ta)_(2)(C,N) synthesized by carbothermal reductionnitridation was used as a novel inhibitor,and its effects on the microstructure and mechanical properties of the cemented carbides were investigated.The results showed that the cemented carbides containing(Cr,Mo,Ta)_(2)(C,N)outperformed its counterpart comprising the traditional inhibitors in comprehensive mechanical properties,which was mainly attributed to the better inhibition performance provided by the(Cr,Mo,Ta)_(2)(C,N) solid-solution powders.With the content of(Cr,Mo,Ta)_(2)(C,N) increasing from 0 wt% to 1.25 wt%,the average grain size of WC in the cemented carbides decreased from 0.85 to 0.60 μm firstly,and then increased to 0.64 μm.With 1.00 wt%(Cr,Mo,-Ta)_(2)(C,N) addition,the cemented carbides with the best performance of hardness(HV_(30)) of 15.55 GPa,transverse rupture strength of 4272 MPa,fracture toughness of13.91 MPa·m1/2 were obtained.The electron backscattered diffraction(EBSD) measurements showed that cemented carbides with(Cr,Mo,Ta)_(2)(C,N) processed more amount of∑2 boundary compared with the other specimens,which contributed to better fracture resistance.

硬脂酸-醇溶性聚氨酯树脂新型成型剂的应用研究

本文以聚乙二醇、硬脂酸、醇溶型聚氨酯树脂、二丁酯、硬酯酸聚氧乙烯酯为原料,通过乙醇溶解试验、过筛试验及滚筒试验,开发出一种以硬脂酸与醇溶型聚氨酯树脂为主的新成型剂,两者的质量比为1∶1。新成型剂能够满足现代喷雾干燥工艺要求。与聚乙二醇、石蜡及顺丁橡胶相比,采用新成型剂制备的混合料具有良好的流动性(33 s/25 cm^(3))与较高的松装密度(3.27 g/cm^(3)),压制相同试样条的情况下,具有较低的压制压力(15.5 kN),试样条烧结后具有均匀的微观结构,且烧结后具有较低的残碳量(0.024%),是一种理想的新型硬质合金模压成型剂。

不同粘结相WC基硬质合金微观结构与性能

以碳质量分数为理论含碳量的WC为硬质相,在1450℃下通过气压烧结制备WC-20Fe,WC-20Ni和WC-20Co硬质合金,通过X射线衍射、扫描电子显微镜、电子探针和力学性能测试研究了不同金属粘结相对烧结硬质合金微观结构和力学性能的影响。结果表明:WC-20Fe合金出现η脱碳相(Fe_(3)W_(3)C),W在粘结相Fe中的溶解度仅有1.915%(质量分数),WC晶粒尺寸最小。WC-20Ni合金渗碳出现石墨相(C),W在粘结相Ni中的溶解度达到10.753%(质量分数),WC晶粒尺寸最大,合金硬度最小。WC-20Co合金为正常两相区组织(WC+γ),具有最高抗弯强度2720 MPa和最大硬度934.41 kg∙mm^(-2)。所有合金断裂模式均为脆性断裂和沿晶断裂,WC-20Co合金断口出现明显的粘结相撕裂。

超细WC和细WC/Co添加对WC-10Co硬质合金微观结构与力学性能的影响

在粒径为0.5μm的超细碳化钨(WC)粉体表面包覆钴(Co)纳米颗粒获得细WC/Co,将细WC/Co、粗WC和Co粉通过球磨混合均匀,压制成型后在1420℃下真空烧结1 h,得到WC-10Co硬质合金。借助扫描电子显微镜、透射电子显微镜、万能试验机等对比研究细WC/Co和超细WC对WC-10Co硬质合金微观形貌和力学性能的影响。结果表明:相比于超细WC,细WC/Co促进合金的致密化,并形成双晶结构。添加细WC/Co和超细WC制备的硬质合金的平均晶粒度分别为2.18μm和3.57μm。细WC/Co的添加会降低晶粒生长速度并抑制细晶完全溶解,而粗晶通过缺陷辅助生长及溶解-析出生长机制生长为表面阶梯状的缺角三棱柱形;硬质合金的硬度和断裂韧度得到提升,二者分别为1131HV 30和22.1 MPa·m^(1/2),而在1131HV 30同等硬度下,其断裂韧度比线性拟合的断裂韧度高27.7%。机理分析认为,超细WC的添加会导致异常晶粒产生,不利于性能;而细WC/Co的添加能够同时形成双晶结构和均匀的钴相分布结构,降低晶粒缺陷,提升综合力学性能。

钴铁镍复合黏结相超细硬质合金显微组织与性能

钴作为硬质合金应用最广泛的黏结剂,存在资源稀缺、成本高昂以及WC-Co硬质合金耐腐蚀性能较差等问题,综合考量生产成本与改善性能,本研究采用铁镍部分代替钴组成复合黏结剂,以其制备超细硬质合金,研究其显微组织和力学、耐蚀耐磨性能的关系。结果表明,黏结相中Fe/Ni质量分数比增加,使得合金WC晶粒细化和黏结相分布不均,合金的硬度和抗弯强度分别提高与降低。合金在中性NaCl溶液中的耐腐蚀性能评估采用极化曲线测试与浸泡实验,黏结相添加Ni能提高合金耐蚀性,归因于Ni的钝化特性与促进腐蚀产物膜的形成。硬质合金摩擦系数和磨损率与Fe/Ni质量比呈负相关,合金耐磨性的提高主要归因于黏结相的强度增强和WC晶粒细化合金硬度提高。